Merge bitcoin/bitcoin#26996: test: Flatten miniwallet array and remove random fee in longpoll

fa0abcd test: Flatten miniwallet array and remove random fee in longpoll (MarcoFalke)

Pull request description:

  * Using a single MiniWallet is enough.
  * A random fee isn't needed either.

ACKs for top commit:
  theStack:
    re-ACK fa0abcd

Tree-SHA512: 77b99885b3f0d325d067838122114be57ec999ebc82912de6a22c33e2ba28a341c5e053c5bbc424b9922c2616562289a57c7156bd3b431d779182c2e472da59c

Author: fanquake

test/functional/mining_getblocktemplate_longpoll.py

@@ -4,7 +4,6 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test longpolling with getblocktemplate."""
 
-from decimal import Decimal
 import random
 import threading
 
@@ -47,28 +46,25 @@ def run_test(self):
         thr.join(5)  # wait 5 seconds or until thread exits
         assert thr.is_alive()
 
-        miniwallets = [MiniWallet(node) for node in self.nodes]
+        self.miniwallet = MiniWallet(self.nodes[0])
         self.log.info("Test that longpoll will terminate if another node generates a block")
-        self.generate(miniwallets[1], 1)  # generate a block on another node
+        self.generate(self.nodes[1], 1)  # generate a block on another node
         # check that thread will exit now that new transaction entered mempool
         thr.join(5)  # wait 5 seconds or until thread exits
         assert not thr.is_alive()
 
         self.log.info("Test that longpoll will terminate if we generate a block ourselves")
         thr = LongpollThread(self.nodes[0])
         thr.start()
-        self.generate(miniwallets[0], 1)  # generate a block on own node
+        self.generate(self.nodes[0], 1)  # generate a block on own node
         thr.join(5)  # wait 5 seconds or until thread exits
         assert not thr.is_alive()
 
         self.log.info("Test that introducing a new transaction into the mempool will terminate the longpoll")
         thr = LongpollThread(self.nodes[0])
         thr.start()
-        # generate a random transaction and submit it
-        min_relay_fee = self.nodes[0].getnetworkinfo()["relayfee"]
-        fee_rate = min_relay_fee + Decimal('0.00000010') * random.randint(0,20)
-        miniwallets[0].send_self_transfer(from_node=random.choice(self.nodes),
-                                          fee_rate=fee_rate)
+        # generate a transaction and submit it
+        self.miniwallet.send_self_transfer(from_node=random.choice(self.nodes))
         # after one minute, every 10 seconds the mempool is probed, so in 80 seconds it should have returned
         thr.join(60 + 20)
         assert not thr.is_alive()